Fuel injectors for internal combustion engines are well known. Such devices are solenoid-driven valves employed for metering fuel in timed pulses from a high-pressure source such as a fuel rail into either the air intake manifold entrance ports for the individual engine cylinders (“port injection”) or directly into the firing chambers (“direct injection”). In a direct injection system, to achieve high-quality combustion and high fuel efficiency, it is important that the injected fuel be vaporized virtually instantaneously as it exits the injector tip, preferably without striking the walls of the engine cylinder or the top of the piston. Thus, it is important that the fuel be precisely directed and highly atomized as it leaves the injector tip so that it may be mixed with the intake air in the optimum ratio for combustion.
For improved atomization, it is well known to divide the exiting fluid jet into a plurality of jets and to impart high turbulence to the jets by use of a director plate.
In a pressure-swirl atomization configuration, such a that disclosed in U.S. Pat. No. 6,202,936 and U.S. Pat. No. 6,382,533, a director plate is located upstream of the valve and seat. On the exterior periphery of the valve needle, diagonally running swirl channels, tangential to the seat orifice is provided in the director plate. The swirl channels empty into a swirl chamber from which the fuel is conveyed to the valve seat. When the valve is lifted from its seat, fuel flows past the valve and through the seat orifice. Because fuel pressure begins to drop above the valve seat as the fuel begins to flow through the swirl channels, and because of the swirl induced by the tangentially positioned swirl channels, the fuel is discharged from the injector in a hollow, conical sheet pattern. A drawback to this configuration is that other spray patterns, which may be more desirable in applications where precise placement of the fuel spray is needed, cannot be achieved.
In a multiple-hole plain orifice atomization configuration, a variety of spray patterns can be achieved. In such a configuration, the fuel director plate both assists in metering flow through the valve, by providing a fixed total flow area, and controls spray atomization and pattern. The director plate is disposed downstream of the valve head and seat. When the injector valve is retracted upon opening, fuel flows around the valve head and seat and then makes an abrupt turn, to flow in a radially outward direction toward multiple discharge holes. Typically, in a multiple hole director plate, the holes are arranged in a ring or other groupings to produce the desired pattern spray pattern. The axes of the holes may be inclined outwards or inwards from the axis of the fuel injector or may be tangentially inclined. The abrupt turn made by the fuel after passing by the seat increases the instability of the individual fuel streams exiting the director plate holes, thereby increasing the level of spray atomization. Moreover, the spray pattern is not limited to a conical sheet as in the case of pressure-swirl atomization configuration. As disclosed in U.S. Pat. No. 6,405,945 and U.S. 2003/0141385, the fuel director plate is located downstream of the valve head and seat, and the fuel is redirected radially outward through channels toward discharge holes on the bottom side of the director plate. The radial channels in these configurations are of a constant width and effective cross-sectional area. Thus, while various spray patterns can be achieved by varying the discharge hole pattern in the director plate, a drawback to this configuration is that the velocity of the fuel stream decreases as it flows radially outward through the director plate channels.
It is a principal object of the present invention to increase the level of atomization of fuel being ejected from the tip of a fuel injector in an internal combustion engine by accelerating the fuel stream by directing the stream radially inward through tapered flow channels to thereby accelerate the fuel stream.